The present invention relates to an addition type polyimide resin raw material composition having high heat resistance, or high heat resistance and high corrosion resistance, a composition and molded object containing a prepolymer, a prepolymer, a curing method thereof, and a coating material using the addition type polyimide resin, a polyimide resin paint, a prepreg for a fiber-reinforced resin composite material excellent in moldability and a method for producing and a method for curing a fiber-reinforced polyimide composite material.
A polyimide resin is widely used in various fields such as a paint and coating material represented by a matrix resin for various fiber-reinforced resin composite material (FRP) since the polyimide resin has excellent heat resistance and excellent corrosion resistance against inorganic and organic strong acid, weak acid, strong alkali and weak alkali and the like. However, the polyimide resin usually has a defect regarding molding that it has a inferior flowability even at high temperature.
The polyimide used as a matrix resin for a fiber-reinforced resin composite material is usually an addition reaction type polyimide which is cross-linked and cured in final process after impregnation of the fiber with the resin. The representative example of such polyimide includes PMR-15 T. T. Serafini; JOURNAL OF APPLIED POLYMER SCIENCE, 16, 905(1972)!. PMR-15 is a polyimide in which the terminal stopper is 5-norbornane-2,3-dicarboxylic anhydride (commonly known as a nadic anhydride) and the main chain is made by condensation of benzophenone tetracarboxylic anhydride and diaminodiphenylmethane, and the reaction in the final stage of curing process progresses by ring opening addition reaction of nadic acids at both ends, therefore, it is said that no volatile component is formed during the reaction, so PMR-15 is widely used as a matrix resin for a fiber-reinforced composite material. However, PMR-15 has a problem that moldability and physical properties of the composite material decrease since pealing occurs between layers of a FRP plate due to cyclopentadiene generated by pyrolysis of the terminal stopper portion in the post process which is called as post cure and conducted after curing of the resin in which heat treatment is conducted at a temperature of not lower than 300.degree. C. to enhance the heat resistance. Further, PMR-15 has also a problem that the pre-curing temperature can not lowered to not higher than 290.degree. C. since nadic anhydride is used as the terminal stopper, and this problem also makes molding difficult.
For molding of a large scale fiber-reinforced composite material, what is called autoclave is generally used which can generate high temperature and high pressure condition in pre-curing. In such molding method, there are used organic supplementary materials for molding such as a bag film, sealant, packing and the like for what is called vacuum bagging which enables uniform pressurization in an autoclave. Therefore, these supplementary materials should be made of a special heat resistant resin when pre-curing temperature is high, then, there occurs difficult problems such as increasing of cost, lowering of physical properties by large thermal residual strain due to high temperature molding. Namely, molding of the polyimide has a lot of difficult problems, therefore, lowering of the pre-curing temperature is an important subject.
Further, when a fiber-reinforced resin composite material is used as a structural component or the like, strength in wet condition as well as in dry condition is very important, especially when a fiber-reinforced resin composite material is used as a structural component in aerospace apparatus filed, strength in wet condition is regarded as important. In general, there is a tendency that the strength of a resin material decreases in wet condition, therefore, improving the strength in wet condition is an important subject of the fiber-reinforced resin composite material.
The polyimide resin has an excellent corrosion resistance against acids and alkalis, and is widely used in various fields which requires corrosion resistance. However, the polyimide resin has a problem that it does not have sufficient corrosion resistance against Lewis acid and Lewis base generated for example in plating field or the like which are defined by Lewis acid-base concept, particularly against non-aqueous Lewis acid and Lewis base such as molten aluminium salts (Al.sup.3+, Cl.sup.-).